We propose to examine two proteinaceous toxins which stimulate release of the neurotransmitter, acetylcholine (ACh). We have found a series of toxins of this sort, and plan now to examine two: Beta-leptinotarsin-d, isolated from the hemolymph of Leptinotarsa decemlineata, and Beta-leptinotarsin-h, from L. haldemani. These toxins seem to stimulate release by forcing open the Ca+2 channel in presynaptic terminals. We shall complete the purification of the toxins to homogeneity, and shall study the purified toxins to define their molecular weight, subunit structure, and amino acid composition. The action of the toxins on the Ca+2 channels of mammalian synaptic terminals will be examined. The binding of toxins to synaptosomes will be measured. Active derivatives of the toxins will be prepared and labeled with either fluorescent or radioactive agents. These derivatives, once properly purified and characterized, will be used to localize the site of their binding (by histochemical techniques) and to detect the receptor for the toxin (by chemical means). Using the labeled toxins as tools, we shall begin to study the receptors for these toxins. These studies should give us more information on the mechanisms controlling release of neurotransmitters, and will help us to understand errors of release which may occur in disease.